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help me understand crank bearings - thin wall, thick wall, high crush

IowaRV9Dreamer

IowaRV9Dreamer

Well Known Member
I've ordered the Lycoming maintenance library from Tdata, but it hasn't come yet...

I mic'd my crank and cam last night. As near as I can tell, the crank is near the top limit of M003, which is what is says on the tag. That means it is 0.003 smaller than a nominal new crank.

Looking at the Lycoming Table of Limits in the overhaul manual, I see there are two bearing types listed: "thin wall (0.09 approx wall)" and "thick wall (0.16 approx wall)".

Looking in the parts catalog for my O-320-E2A, I see two types of bearings - both are marked "crankshaft bearing" and are listed for my model. One has a ** after it that says "thin wall, high crush".

So my question is - when do you use a regular bearing, and when do you use a "thin wall, high crush" bearing? Is the case the same for either one?

Also a related question: The Parts Catalog has a "Oversize and Undersize Parts Listing" that lists both bearings... and it shows what sizes are available. Would I purchase a M03 bearing (aka "undersize") or an "oversize" Pxx bearing. The oversize come in P02 or P05.

All of the above discussion is for the middle and rear bearings. The large, front one-piece bearings don't seem to have a thin/thick/high crush thing going on. I wonder why?

I know there is a Lycoming Service Letter that will help, and I'll get it soon, but I was hoping someone would have some good, general info.
 
bearings

With a dial caliper measure across the bearing bore in one side of the case. Engage the caliper just enough to get a measurement, as close to the case split surface as possible. This does not need to be a super accurate measurement. Now measure the crank main bearing diameter. Subtract the crank dimension from the case dimension and divide the result by two. If the answer is near .090, you need the thin wall bearing. If near .160 you need thick.
I believe the center and rear main heavy bearings are both doweled, but do not have the information in front of me to confirm this.
Some of the E series have the four piece front main bearing. You need to confirm what you need via the parts book.
 
bearings

Checked my notes and the parts book on this:
E2A uses two piece front main bearing, same as most except for a few E series.
Center main and rear main are thin-high crush bearings, no dowels at these locations.
If the engine was a certified engine the above is correct, if it was an Experimental engine, who knows. If experimental and the center and rear main bores have dowel pins, then it has been modified for heavy wall bearings.
 
Thanks Jim - the connection between dowels and thick bearings what what I was missing. I'll inspect and measure my case and see what was done to it.

You are correct that my engine uses the two piece (aka large) front main bearing. It supposedly came out of a Cherokee.

Thanks again!

PS - thanks to the unseen moderator who deleted the unhelpful comment :)
 
Lycoming

My Lycoming info shows that the E2A was a Cherokee 140 engine.
No need to measure if it came out of the Cherokee. No dowels means thin high crush bearings on center and rear.
I got my bearings from Dart Aircraft 888-753-1810. Very helpful and fast service. If they don't have parts in stock they will drop ship from ECI usually same day. make sure you're sitting down when you get the price on the bearings.
 
I also had my crank cut as it was at the bottom of service limits and now is new limits M03. My case is an early Wide Deck from 1966 that hasn't been cut before.My center and rear main bearings are thick wall Pinned&Dowled 10124.When the case is serviced the main bores are cut as well as the cam bores,then the two half's are milled & lapped back to std size.The price of the bearings are a little more than stock but you will have a new limits engine.My crank is now M03/M03 and require both M03 replacements on all main/rod bearings.Your information will be on the yellow tag as well as the 8130-3 from the machine shop.There are sub differences within the dowled part numbers for stepped and un stepped dowled depending on what the machine shop put back after service.I bought Nos 10124M03 bearings as well as M03 nose bearings to go back in.Did you save every nut and washer from the tare down of your engine?What numbers came out?
 
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rhill said:
Did you save every nut and washer from the tare down of your engine?What numbers came out?
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I bought the engine as a disassembled but yellow tagged core. I have tags on the crank, cam, case, and lots of other parts from well known specialty shops. Unfortunately I don't have any 8130s, and the work was done in 2007 so there are no other records.

The tags do show the crank as M003/M003.

I may send the case to Divco for a dimensional check, just to be double sure I'm good to go.
 
case

The information in post #7 is incorrect. Crankcase halves are either lapped or milled on the parting surface. They are then either honed or line bored to restore the cam bores and bearing bores. For certification, all dimensions, including accessory case dowel locations, must be to an established tolerance. Therefore there should be no need for any work on the accessory case or sump to insure that they fit. If the case does not meet certification standards, accessory case fit on dowels could be a problem.
 
jrs14855 said:
The information in post #7 is incorrect. Crankcase halves are either lapped or milled on the parting surface. They are then either honed or line bored to restore the cam bores and bearing bores. For certification, all dimensions, including accessory case dowel locations, must be to an established tolerance. Therefore there should be no need for any work on the accessory case or sump to insure that they fit. If the case does not meet certification standards, accessory case fit on dowels could be a problem.
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I stand corrected,Thank you,I have edited post#7 with the correct info.In my case,Crank Case Services requested the oil pan and accessory housing for tagging .The issue comes with "Deck Height",cracks can be welded,studs replaced,there are only so many times the parting half's can be milled and be in certified limits. AD's are a another area of compliance, Lycoming constantly changes what should be replaced when overhauling these engines see Lycoming SB240 2012, I'm told Lycoming now wants hydraulic units replaced not reconditioned.I liked the idea that they were matched for opening pressure and I think you can send in new units for this service
 
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Great info in this thread, thanks.

I went and pulled out the case and my old engine parts and was surprised to see that there are in fact dowels installed on the mid and rear races. I even found the original bearings and they are in fact "thick".

It is likely that this isn't a first run engine, so if the dowels aren't original, they may have been added at some point. I think there is a Lycoming SI about them.

Even though the case is tagged by Central Cylinder to meet certification standards, I am going to send it to Divco to be sure.

Hoo Boy!
I think the front bearing is 18A26093-M03, $162 each half and the rest are 18D26096-M03, only $36 each piece. So $468 just for crank bearings!
 
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IowaRV9Dreamer said:
I bought the engine as a disassembled but yellow tagged core. I have tags on the crank, cam, case, and lots of other parts from well known specialty shops. Unfortunately I don't have any 8130s, and the work was done in 2007 so there are no other records.

The tags do show the crank as M003/M003.

I may send the case to Divco for a dimensional check, just to be double sure I'm good to go.
Click to expand...

Its the responsibility of the engine assembler to make sure each part is clean and meets all Ad's,SI's and specifications for assembly.Who is going to build your engine? If its an experienced builder he should be able to mic out every component before it goes together,then run it on a test cell for an hour,start a log book for the engine.It's great if you can help and be part of the process,take lots of photos,save box's and paper work.
 
IowaRV9Dreamer said:
Great info in this thread, thanks.

I went and pulled out the case and my old engine parts and was surprised to see that there are in fact dowels installed on the mid and rear races. I even found the original bearings and they are in fact "thick".

It is likely that this isn't a first run engine, so if the dowels aren't original, they may have been added at some point. I think there is a Lycoming SI about them.

Even though the case is tagged by Central Cylinder to meet certification standards, I am going to send it to Divco to be sure.
Click to expand...

Call for pricing,I was told $700 is a flat fee,if they have to do everything they can to save a case or just look at it and give it there blessing $700 + shipping both ways. Another point is Crankshaft end play,this is set in the case.The engine will need to be built up to this point and checked if it needs to be adjusted the case half's will need to go back and be welded&milled for the right clearance.I'd hold off till you check with your builder IMHO.Check on the back of the old bearings for the part numbers will be at the top on one side.
 
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IowaRV9Dreamer said:
Great info in this thread, thanks.

I went and pulled out the case and my old engine parts and was surprised to see that there are in fact dowels installed on the mid and rear races. I even found the original bearings and they are in fact "thick".

It is likely that this isn't a first run engine, so if the dowels aren't original, they may have been added at some point. I think there is a Lycoming SI about them.

Even though the case is tagged by Central Cylinder to meet certification standards, I am going to send it to Divco to be sure.

Hoo Boy!
I think the front bearing is 18A26093-M03, $162 each half and the rest are 18D26096-M03, only $36 each piece. So $468 just for crank bearings!
Click to expand...

Sounds about right,don't forget to price out the rest of Lycoming SI 240 its an eye opener for sure

See post #16 for corrections, I found NOS M03 bearings on ebay and can check with my guy if you have the original part number
 
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rhill said:
Sounds about right,don't forget to price out the rest of Lycoming SI 240 its an eye opener for sure
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He's just getting started, don't discourage him...!
Sent him all the SIs and SBs I knew of except the last one that cropped up, SB400. Waiting for parts.....again.
 
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flyingriki said:
He's just getting started, don't discourage him...!
Sent him all the SIs and SBs I knew of except the last one that cropped up, SB400. Waiting for parts.....again.
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My apologies. I have no wish to discourage anyone from "Rolling there own". For me its the only way I could get over the cost hump.The FAA allows us to do this for our "Education & Edification" and man they ain't lying! The original post was about bearings and comes down to old engine/new engine question,wile on the phone to Aircraft Specialties,Bob asked me "What parts book do you have?" I gave him the latest PC number,he laughed "H**l Son,you need the old parts book to build the old motor." For me,problem solved so I thought,now for the AD's,Sb's,Si's.SB 400 Teflon end play plugs for the rocker shafts,not expensive,I keep them in the freezer with my engine mounts,extends the cure date.
RHill:)
 
Larry Conway of Aircraft Engine Resources in Brighton IA Put my engine together. He is more than willing to let you watch and help while explaining everything.
 
Thanks for the excellent info. I am in the "gathering info" stage prior to assembly.

The plan is to assemble the engine myself, with another RV pilot (who assembled his) and a local A&P looking on. A nationally respected engine shop a few hours away is proving email support, and when it is done I plan to take it there to use their test cell. I am considering building it there to take advantage of their expertise, but we'll see.

I'm confident in all of the parts (which are all cleaned, tagged) except for the case so I'm going to send it to Divco to have it re-inspected. Sounds like I should temporarily install the crank to check end play first.

The parts price isn't discouraging. Like rhill, I am saving money doing this myself. My main goal at this point is to get a list of parts I need for this build (including any missing hardware) and see if I can get it quoted out. I'm waiting for my Tdata DVD to arrive with latest / current data on it before really beginning.

The "you shouldn't/can't" comments are slightly discouraging but that's the internet. I am extremely mechanical and know that assembling this engine is within my skill set. An yes, this is for "recreation and education". When this engine is done, it will be the equal of any other field overhauled Lyc out there in the certified world... or better :)
 
rhill said:
....... Another point is Crankshaft end play,this is set in the case.The engine will need to be built up to this point and checked if it needs to be adjusted the case half's will need to go back and be welded&milled for the right clearance.....
Click to expand...

It sounds like the approved ECI crankcase modification to add a thrust washer would be better than welding and milling -

CCM24Modify for Installation of TCM Thrust Washer $285.00 $171.00

http://www.eci.aero/pages/repairs_cca.aspx#Modifications
 
az_gila said:
It sounds like the approved ECI crankcase modification to add a thrust washer would be better than welding and milling -

CCM24Modify for Installation of TCM Thrust Washer $285.00 $171.00

http://www.eci.aero/pages/repairs_cca.aspx#Modifications
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If the Crank & Case are from the same core then odds are good the end play is good. Sounds like a good plan,I'm a factory trained Mercedes Tech and have built tons of engines,have done the Mattituck one day school,been at a lot of Lycoming seminars at Oshkosh.Would love to have John or Mahlon be involved and sign off on the build but that's not going to happen.I've toyed with the idea of building this at the Lycoming school in Williamsport,I don't know if they would let me.I can see where no one would want my engine.I'll be involved and document the wazoo out of it,save the box's,tags,receipts,old parts,tons of photos.Sounds like your thinking along the same lines.
RHill
 
Engine parts

I'm building an 0-360 and have acquired enough new parts to build 2 to 3 engines,in some things,like oil pump gear sets I have 6. I only buy new in the box,many with 8130-3s. I've been doing this for four years,its an obsession mixed with Hoarders syndrome,Lycoming,Superior,some ECI not so much.I love new Lycoming in the factory box with 8130-3 just as much as M&M almonds.It's a sickness.I told my wife as soon as I get this flying I'm going to Quit,cold turkey............... its a lie,I can't quit,I've tried.I have no control:eek:.Let me know if you need anything!
RHill
 
The reason for the thick or thin bearings is that when the case halves are flycut or better yet lapped, the bearing journals get ob-longed (out of round), and so the holes need to be bored for the next larger size of bearing. On the 540's and some 360's the mag bearing support bosses (if so equipped) have to be welded up and relocated since the gears will mesh too tightly after the case halves are flycut. If the bearing bore dimensions are too big then they have to be bored for the thick bearings.

If you study the table of limits closely you'll notice that some ob-longing is acceptable.

Most shops flycut because time is money and its a simple setup to flycut a case. But in most cases its completely unnecessary, because they usually remove too much material.

Personally I don't like any of the case shops. When one gets a case back from a large machine shop mentioned in this thread and decks have been scotch brighted, that tells you they're not thinking about the flatness of the deck. This will guarantee eventual oil leaks at the cylinder bases.
 
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rocketbob said:
The reason for the thick or thin bearings is that when the case halves are flycut or better yet lapped, the bearing journals get ob-longed. On the 540's and some 360's the mag bearing support bosses (if so equipped) have to be welded up and relocated since the gears will mesh too tightly after the case halves are flycut. If the bearing bore dimensions are too big then they have to be bored for the thick bearings, and the thicker bearings have to be used.
Click to expand...

Bob,How is the lapping done,remove the studs a little valve grinding compound and rub the two half's together?Or on a standard,1/2 at a time?I'm tossed on sending my case in,it has never been cut,but I do want the yellow tag........
I'm afraid
 
Yo, rhill. If the case shows no fretting and the crank/cam holes dimension out, then it probably needs no line boring or surfacing. What it does need regardless is a good crack inspection. If you can't do that I would shop it. They will also clean areas you probably wouldn't. Just so they don't go bead blast crazy. Worst thing about doing engines at home is what it does to my hands because I don't do enough to justify proper deluxe cleaning equipment.
 
A good shop also knows all the ADs, SIs and SBs that are needed. Mine needed the extra hole in the oil pump pad and they machined that whole area flat. Took some new studs and something wlse I'm forgetting.... Not the kind of stuff an amateur like myself would know to ask for.

Same with the crank. Took several bulletins and a chunk of change to be yellow tagged, but was - thank goodness!
 
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Thanks Dave,Rik. I spent $1100 on the crank/cam tags.I'm told the case is one price $700 to $750. I agree with the crack check,I don't see the need to cut the half's,some lite lapping I understand.My case will need what it needs,I just don't want the standard treatment if I don't need the standard treatment.Most automotive machine shops have hot tanks and high pressure Roto-jet parts cleaners for $100 these can spin in there all day,I think they use Cascade dish detergent and hot water.I would love to hear what Rocket Bob does if he is not generally happy with the big boys. My wife will be out of town later this week,I think these will fit in my dish washer....HUM!
 
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rhill said:
Bob,How is the lapping done,remove the studs a little valve grinding compound and rub the two half's together?Or on a standard,1/2 at a time?I'm tossed on sending my case in,it has never been cut,but I do want the yellow tag........
I'm afraid
Click to expand...

Lapping compound on a large lapping plate at a friends machine shop.

You could also do it with a large oiled sheet of sandpaper on a granite surface plate.
 
First thing I do after removing the engine is put it on the stand, remove the mags/wires, and cover up the magneto holes. Then cover the whole engine with paint stripper. The stuff I use is SV-35, and spray it on with a cheap harbor freight electric sprayer. SV-35 is good because it is peroxide based and will not burn your hands, and cleans up with water. Then pressure wash. After stripping, pressure wash, and blowdry, start disassembly. Once everything is disassembled I just clean the cases in my solvent washer, then spray with phosphoric acid and rinse several times to get the case prepped for alodine. I have a large bucket of alodine and will dip the case halves after all the work is done.
 
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Case

Thanks Bob, Is striping all paint off the case necessary for crack inspection?Do you pull all the allen plugs out of the oil bores before you alodine? I take it your alodineing the machined services also if your dipping as apposed to brushing the outer case. The big question where should I be looking for cracks on a -36 case?
RHill
 
rhill said:
Thanks Bob, Is striping all paint off the case necessary for crack inspection?Do you pull all the allen plugs out of the oil bores before you alodine? I take it your alodineing the machined services also if your dipping as apposed to brushing the outer case. The big question where should I be looking for cracks on a -36 case?
RHill
Click to expand...

I strip everything just because I want everything squeaky clean.

Yes you want to clean the galleries out so I open those up and use a long brass bristle brush to clean them out. I've only seen one cracked Lycoming case and that was next to a stud, on one of the older style cases where the thru bolt was threaded into the other half.
 
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